The present invention relates to a non-volatile memory system for use in a vehicle and specifically to an electronic system having improved storing procedures for storing data to a non-volatile memory.
As the use of electronics in vehicles increases, so does the need for and use of non-volatile memories in such systems. Non-volatile memories are currently used in vehicle electronic systems for storing program instructions for various microcontroller processes, as well as variable data that must be stored in a non-volatile memory to avoid losing the data each time the vehicle's ignition is turned off. For example, such data may include the odometer data of an electronic odometer, the mileage travelled since a last reset of the trip distance meter, compass calibration data, data representing the temperature sensed at the time the ignition was last turned off, data representing the lapsed time from the last timer reset as of the time the ignition is last turned off, and any other data that is advantageously stored in memory for recall after the ignition is turned on again.
In order to store data in a non-volatile memory with the ignition off, the power supply modules for the electronic systems utilizing non-volatile memories must have connections to both the vehicle's ignition power supply line and to the vehicle's battery. Providing two powerline connections to a component in a vehicle increases the cost of including such an electronic accessory in the vehicle. Further, when the electronic accessory is placed in a location in the vehicle that is further away from the instrument panel, a connection to both the ignition and the battery may not be possible without increasing the installation cost of the accessory to a level that makes it impractical to add the accessory in the vehicle. Additionally, each power supply line typically requires transient protection circuitry to isolate the electronic component from any input noise on the powerline and from radiated output emissions. Further, a switch-over circuit must be included in the accessory power supply to switch the power supply from one line to another. All of these added components associated with the inclusion of two different power supply lines significantly increases the production costs for the electronic accessory. In the automotive environment where vehicles are mass-produced, the added costs associated with providing two powerlines to a single electronic accessory can be significant.
Non-volatile memories of the type used in vehicles have typically had a limited number of data stores per lifetime. A typical number of stores per lifetime for a non-volatile memory had been 10,000 stores. Thus, it has been necessary to limit the number of data stores that are made to a vehicle's non-volatile memory to ensure that the non-volatile memory would be functional throughout the lifetime of the vehicle. Because of these limitations, vehicle electronic systems have typically only stored data in the non-volatile memory upon the detection of the turning off of the vehicle's ignition.
Another problem associated with vehicle electronic accessories that require a connection to the battery power supply line is that the electronic accessory could get locked in a failure mode and, if the electronic accessory utilizes significant amounts of power, a vehicle's battery could become completely drained.